In a liquid crystal panel, a polarizing plate is used to control optical rotation of light beams that pass through liquid crystals. Conventionally, in such a polarizing plate, a polarizing plate obtained by dying a resin film, such as a polyvinyl alcohol or the like with iodine or a dichromatic dye and stretching the film in one direction has been widely used. However, there has been a problem that the aforementioned polarizing plate is poor in heat resistance and light resistance depending on the kind of the dye or the resin film. Moreover, film manufacturing equipment has become bigger as liquid crystal panels become bigger, which has become a problem.
In contrast, a method for forming a polarizing film by casting a liquid crystalline coating solution containing a lyotropic liquid crystal compound on a substrate, such as a glass plate or a resin film and the like to orient the lyotropic liquid crystal compound is known. The lyotropic liquid crystal compound forms supramolecular aggregates exhibiting liquid crystallinity in the solution, so that the long axis direction of the supramolecular aggregates is oriented in a flowing direction when flowing after applying shearing stress onto the liquid crystalline coating solution containing this. Examples of such lytropic liquid crystal compounds include azo compounds (JP 2006-323377 A). Lyotropic liquid crystal compounds based polarizing films do not need to be stretched and are easy to have a greater thickness because of no shrinkage in a width direction by stretching. Further, the lyotropic liquid crystal compounds based polarizing films are expected to have potential because the thickness can be reduced significantly.
However, the polarizing film obtained by casting a liquid crystalline coating solution including a conventional azo compound has a drawback that fine crystals are separated out in the film in a drying process, so that transparency is deteriorated due to an increase in haze (light scattering) of the polarizing film. Thus, a liquid crystalline coating solution including a novel azo compound which has resolved this problem has been demanded.
It is an object of the present invention in a polarizing film obtained from a liquid crystalline coating solution including an azo compound to provide a liquid crystalline coating solution including a novel azo compound which has resolved the drawback of the deteriorated transparency caused by an increase in haze (light scattering) of the polarizing film because of the separating of fine crystals in the film.